This invention relates to computer disc drives and more particularly to a power management system for disc drivers of spin and actuator motors during power failure.
To provide for data integrity, most disc drives park their read/write heads on a special landing zone when spinning up or down. To park the heads without external power during a power fault condition, the inertia of the spindle motor is used to provide power to the actuator for parking the heads. Such a retract power regeneration system is as follows.
The inertia of the spindle is converted to electrical power by rectifying the back electromotive force (e.m.f.) of the spindle motor. In typical disc drive designs, represented in the circuit of FIG. 1, the spindle motor 10 is a three phase brushless DC motor. The full wave rectifier 12 has six diodes 14, 16, 18, 20, 22 and 24.
In normal operation, Vcc is high and diodes 26 and 28 are conducting, and these two diodes provide for power to the spindle power amplifier 30 and the actuator power amplifier 32.
When power is lost while the spindle is running, diodes 26 and 28 are non-conducting; diode 26 blocking power supply voltage Vcc from the spindle power amplifier 30 and diode 28 blocking Vcc from the actuator power amplifier 10. The back e.m.f. of the spindle motor meanwhile provides voltage to the actuator 33 for parking.
Thus during power loss, diodes 26 and 28 are required to keep from diverting energy from the spinning spindle motor into the other circuits 34, all of which energy is needed for energizing the actuator power amplifier 32.
The DC voltage available for energizing each the spindle and actuator driver amplifiers 30 and 32 is less than Vcc by one diode voltage drop, i.e. at least a 0.6 volt drop in a silicon integrated circuit. This diode voltage loss imposes a major design constraint for the spindle motor 10 and the driver amplifiers 30 and 32.
It is an object of this invention to provide a disc drive power management system that over comes the above noted short comings of prior art disc drives.
It is a further object of this invention to provide a disc drive power management system that circumvents the need for blocking diodes interposed between the DC power supply and the power amplifiers for driving the spindle and actuator motors.